Gas generant compositions

ABSTRACT

A novel compound, tris (5-amino tetrazolo) triazine is used for example, as a gas generating fuel. A method of making the compound is also provided. A gas generating composition, containing the novel compound as a fuel, and an oxidizer is also provided. The novel compound may be contained within a gas generant composition  12 , within a gas generator  10 . The gas generator  10  may be contained within a gas generating system  200  such as an airbag inflator  10  or seat belt assembly  150 , or more broadly within a vehicle occupant protection system  180.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/798,206 filed on May 5, 2006.

TECHNICAL FIELD

The present invention relates generally to gas generating systems, andto gas generating compositions employed in gas generator devices forautomotive restraint systems, for example.

BACKGROUND OF THE INVENTION

The present invention relates to gas generant compositions that uponcombustion produce a relatively smaller amount of solids and arelatively abundant amount of gas. It is an ongoing challenge to reducethe amount of solids and increase the amount of gas thereby decreasingthe filtration requirements for an inflator. As a result, the filter maybe either reduced in size or eliminated altogether thereby reducing theweight and/or size of the inflator. Additionally, reduction ofcombustion solids provides relatively greater amounts of gaseousproducts per gram or unit of gas generating composition. Accordingly,less gas generant is required when greater mols of gas are produced pergram of gas generant. The result is typically a smaller and lessexpensive inflator due to reduced manufacturing complexity.

Yet another concern is that the compositions must exhibit burn ratesthat are satisfactory with regard to use in vehicle occupant protectionsystems. In particular, compositions containing phase stabilizedammonium nitrate may exhibit relatively lower burn rates requiringvarious measures to improve the burn rate. Accordingly, the developmentof energetic fuels is one ongoing research emphasis whereby the lessaggressive burn characteristics of preferred oxidizers such as phasestabilized ammonium nitrate are accommodated and compensated.

SUMMARY OF THE INVENTION

The above-referenced concerns are resolved by gas generators or gasgenerating systems containing a novel fuel constituent, methoxycarbonyl-5 amino tetrazole, within novel gas generant compositions. Itwill be appreciated that the novel compound formed in accordance withthe present invention may have applications other than as a gas generantconstituent.

An optional second fuel may be selected from tetrazoles and saltsthereof, triazoles and salts thereof, azoles and salts thereof,guanidines and salts thereof, guanidine derivatives, amides, andmixtures thereof. An oxidizer is selected from metal and nonmetalnitrates, nitrites, chlorates, perchlorates, oxides, other knownoxidizers, and mixtures thereof.

In further accordance with the present invention, a gas generator or gasgenerating system, and a vehicle occupant protection systemincorporating the gas generant composition are also included.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view showing the general structure ofan inflator in accordance with the present invention.

FIG. 2 is a schematic representation of an exemplary vehicle occupantrestraint system containing a gas generant composition in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the present invention provides a novel method offorming a nitrogen-containing compound, useful as a fuel within a gasgenerant system, for example. The method may be described by thefollowing steps:

-   1. Providing a solution of 5-amino tetrazole and triethyl amine in    acetonitrile, wherein 5-amino tetrazole and triethyl amine are    provided in roughly equimolar amounts, and acetonitrile is provided    in an amount sufficient to solublize the reactants of this method.    When dissolved in acetonitrile, the mixture becomes a clear    solution.-   2. Adding cyanuric chloride at about 0.3 to 0.4 the molar amount of    the triethyl amine, to a cooled solution of about 0-10 degrees    Celsius.-   3. Stir the mixture and slowly bring to room temperature.-   4. Reflux in a round-bottom flask using the water condenser to form    a product solid.-   5. Cool to room temperature.-   6. Remove the remaining solvent, preferably under vacuum conditions,    wherein residue remains.-   7. Wash the residue with dilute 3N hydrochloric acid to yield a    brown-colored solid.-   8. Dry the solid.

The reaction given below illustrates the formation of this fuel.

To a solution of 5-Amino tetrazole(2.7675 g, 32.5362 mmol)/Triethylamine(4.5614 ml, 32.8615 mmol) in acetonitrile was added cyanuricchloride (2.0 g, 10.8453 mmol) at 0° C. The reaction mixture was slowlybrought to room temperature and stirred for about 30 minutes. Afterabout 30 minutes the reaction warmed and was refluxed for about 24 hrs.The reaction was then cooled to room temperature and the solvent wasremoved under reduced pressure, leaving a residue. The residue waswashed with dilute HCl to yield a white-colored solid. The solid wasthen dried at 105° C. for about 4 hrs.

Infrared (IR) evaluations indicated 3400 cm-1 for N-H, 1635,1525 cm-1for tetrazoles, and 1472,1425 cm-1 for triazine system, therebyconfirming the structure of the product. Differential ScanningCalorimetry (DSC) evaluation resulted in a broad exotherm at 310° C. Thereaction product bums moderately well at higher temperatures.

The reaction product exhibited relatively high energy and when combinedwith oxidizers as described below, also exhibited good bum rates inexcess of 0.4 inches per second, when evaluated as known in the art.

Theoretical Calculation:

With a fuel/oxidizer ratio of 23/77, that is BTU/PSAN in wt %, then thepropellant oxygen balance equals −1.09. This oxygen balance results in a96.4% gas yield and produces 4.04 moles of gas per 100 gm of propellant.

Each fuel is nitrogen-rich, thereby maximizing the non-metalconstituents of the total gas generant composition.

The fuel is provided at about 5-50 wt % and more preferably at about15-30 wt %, of the gas generant composition.

Optional secondary fuels include tetrazoles such as 5-aminotetrazole;metal salts of azoles such as potassium 5-aminotetrazole; nonmetal saltsof azoles such as diammonium salt of 5,5′-bis-1H-tetrazole: nitratesalts of azoles such as 5-aminotetrazole; nitramine derivatives ofazoles such as 5-aminotetrazole; metal salts of nitramine derivatives ofazoles such as dipotassium 5-aminotetrazole; metal salts of nitraminederivatives of azoles such as dipotassium 5-aminotetrazole; nonmetalsalts of nitramine derivatives of azoles such as monoammonium5-aminotetrazole and; guanidiness such as dicyandiamide; salts ofguanidines such as guanidine nitrate; nitro derivatives of guanidinessuch as nitroguanidine; azoamides such as azodicarbonamide; nitratesalts of azoamides such as azodicarbonamidine dinitrate; and mixturesthereof. The secondary fuel can be used within this system as co-fuelsto the primary fuel. If used, the secondary fuel when combined with theprimary fuel constitutes about 5-50 wt % of the gas generantcomposition. By itself, the secondary fuel constitutes 0-45 wt %, andmore preferably about 15-30 wt % when used.

An oxidizer component is selected from at least one exemplary oxidizerselected from basic metal nitrates, and, metal and nonmetal nitrates,chlorates, perchlorates, nitrites, oxides, and peroxides such as basiccopper (II) nitrate, strontium nitrate, potassium nitrate, potassiumnitrite, iron oxide, and copper oxide. Other oxidizers as recognized byone of ordinary skill in the art may also be employed. The oxidizer isgenerally provided at about 50-95 wt % of the gas generant composition.

Processing aids such as fumed silica, boron nitride, and graphite mayalso be employed. Accordingly, the gas generant may be safely compressedinto tablets, or slugged and then granulated. The processing aid isgenerally provided at about 0-15 wt %, and more preferably at about 0-5wt %.

Slag formers may also be provided and are selected from siliconcompounds such as elemental silicone; silicon dioxide; silicones such aspolydimethylsiloxane; silicates such as potassium silicates; naturalminerals such as talc and clay, and other known slag formers. The slagformer is typically provided at about 0-10 wt %, and more preferably atabout 0-5 wt %.

The compositions of the present invention are formed from constituentsas provided by known suppliers such as Aldrich or Fisher Chemicalcompanies. The compositions may be provided in granulated form anddry-mixed and compacted in a known manner, or otherwise mixed as knownin the art. The compositions may be employed in gas generators typicallyfound in airbag devices or occupant protection systems, or in safetybelt devices, or in gas generating systems such as a vehicle occupantprotection system, all manufactured as known in the art, or asappreciated by one of ordinary skill.

As shown in FIG. 1, an exemplary inflator or gas generating system 10incorporates a dual chamber design to tailor containing a primary gasgenerating composition 12 formed as described herein, may bemanufactured as known in the art. U.S. Patent Nos. 6,422,601, 6,805,377,6,659,500, 6,749,219, and 6,752,421 exemplify typical airbag inflatordesigns and are each incorporated herein by reference in their entirety.

Referring now to FIG. 2, the exemplary inflator or gas generating system10 described above may also be incorporated into an airbag system 200.Airbag system 200 includes at least one airbag 202 and an inflator 10containing a gas generant composition 12 in accordance with the presentinvention, coupled to airbag 202 so as to enable fluid communicationwith an interior of the airbag. Airbag system 200 may also include (orbe in communication with) a crash event sensor 210. Crash event sensor210 includes a known crash sensor algorithm that signals actuation ofairbag system 200 via, for example, activation of airbag inflator 10 inthe event of a collision.

Referring again to FIG. 2, airbag system 200 may also be incorporatedinto a broader, more comprehensive vehicle occupant restraint system 180including additional elements such as a safety belt assembly 150. FIG. 2shows a schematic diagram of one exemplary embodiment of such arestraint system. Safety belt assembly 150 includes a safety belthousing 152 and a safety belt 100 extending from housing 152. A safetybelt retractor mechanism 154 (for example, a spring-loaded mechanism)may be coupled to an end portion of the belt. In addition, a safety beltpretensioner 156 containing gas generating/auto ignition composition 12may be coupled to belt retractor mechanism 154 to actuate the retractormechanism in the event of a collision. Typical seat belt retractormechanisms which may be used in conjunction with the safety beltembodiments of the present invention are described in U.S. Pat. Nos.5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546,incorporated herein by reference. Illustrative examples of typicalpretensioners with which the safety belt embodiments of the presentinvention may be combined are described in U.S. Pat. Nos. 6,505,790 and6,419,177, incorporated herein by reference.

Safety belt assembly 150 may also include (or be in communication with)a crash event sensor 158 (for example, an inertia sensor or anaccelerometer) including a known crash sensor algorithm that signalsactuation of belt pretensioner 156 via, for example, activation of apyrotechnic igniter (not shown) incorporated into the pretensioner. U.S.Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein byreference, provide illustrative examples of pretensioners actuated insuch a manner.

It should be appreciated that safety belt assembly 150, airbag system200, and more broadly, vehicle occupant protection system 180 exemplifybut do not limit gas generating systems contemplated in accordance withthe present invention.

It should further be understood that the preceding is merely a detaileddescription of various embodiments of this invention and that numerouschanges to the disclosed embodiments can be made in accordance with thedisclosure herein without departing from the scope of the invention. Thepreceding description, therefore, is not meant to limit the scope of theinvention. Rather, the scope of the invention is to be determined onlyby the appended claims and their equivalents.

1. A compound defined as having the structural formula of:


2. A composition comprising: tris (5-amino tetolo) triazine as a firstfuel, said fuel provided at about 5-50 weight percent; an oxidizerselected from basic metal nitrates, and, metal and nonmetal nitrates,chlorates, perchlorates, nitrites, oxides, and peroxides, said oxidizerprovided at about 50-95 weight percent.
 3. The composition of claim 2further comprising: a second fuel selected from carboxylic acids; aminoacids; tetrazoles; triazoles; guanidines; azoamides; metal and nonmetalsalts thereof; and mixtures thereof, said second fuel provided at about0.1-30 weight percent
 4. A gas generating system containing the compoundof claim
 1. 5. A vehicle occupant protection system containing thecompound
 1. 6. A gas generating system containing the composition ofclaim
 2. 7. A vehicle occupant protection system containing thecomposition of claim
 2. 8. A composition containing the compound ofclaim
 1. 9. A method of forming a compound comprising the steps of:providing a solution of 5-amino tetrazole and triethyl amine inacetonitrile, wherein 5-amino tetrazole and triethyl amine are providedin roughly equimolar amounts, and acetonitrile is provided in an amountsufficient to solublize the reactants of this method; adding cyanuricchloride in about 0.3 to about 0.4 of the molar amount of the triethylamine, to a cooled solution; stir the mixture and slowly bring to roomtemperature; reflux the solution to form a product solid; and removeexcess solvent.
 10. The compound formed by the method of claim
 9. 11. Agas generant composition containing the compound formed by the method ofclaim
 9. 12. A gas generating system containing the compound formed bythe method of claim
 9. 13. A vehicle occupant proton system containingthe compound formed by the method of claim 9.